Viabilities of originally natural O-chromosomal inversion homo- and heterokaryotypes in Drosophila subobscura

Abstract

The influence of epistatic interactions of lethal and non-lethal genes upon viability of Drosophila inversion karyotypes is poorly known. In this paper we present comparative results for viabilities of 21 originally natural O-inversion homo- and 38 heterokaryotypes in a D. subobscura population. We observed strong heterotic effect in viability of O-lethal heterozygotes irrespective of different inversion backgrounds, which indicates a mechanism for protection of a great number of lethal genes. In O-non-lethal heterozygotes the heterotic effect in viability was absent irrespective of different inversion backgrounds. Our results showed a great extent of genetic load and high abundance of O-chromosomal arrangements in the population analyzed. It belongs to the set of central European populations. An epistasis of lethal genes present in O-inversion hetero- and not present in O-inversion homokaryotypes of moderate or low frequencies could be good example for co-adaptation of chromosomal inversions with regard to the genetic load. This represents a more efficient mechanism for limitation of genetic load than alternative mechanisms for protection of lethals. Except for lethal genes, possible epistatic interactions of mildly deleterious (subvital) genes, could also be responsible for limiting the extent of genetic load in natural D. subobscura populations. We demonstrated a non-random distribution of several combinations of viability classes among different O-inversion homo- and heterokaryotypes. As a consequence of that, the viabilities of the O-inversion homokaryotypes compared to heterokaryotypes were significantly higher at low frequencies than in moderate or high frequencies. This shows frequency-dependence as a mechanism of balancing selection for protection of O-chromosomal inversions in natural D. subobscura populations. In addition, the viabilities of the O-inversion homokaryotypes of lower frequency, compared to homokaryotypes of moderate or high frequency, were significantly higher. This again indicates the existence of supergene selection as another mechanism for protection of chromosomal inversions, as co-adapted complexes in natural D. subobscura populations.

Evolution of Chilean colonizing populations of Drosophila subobscura: lethal genes and chromosomal arrangements

“…To compare the chromosomal polymorphism of lethal versus non-lethal arrangements, we carried out a principal component analysis for 11 populations, each divided into two samples (non-lethal and lethal chromosomes): Kamariste (K and KL), Zanjic (Z and ZL), Petnica (P and PL), Djerdap I (DI and DIL) (collected in 2001) and Djerdap II (DII and DIIL) (collected in 2002) from the Palearctic region (Zivanovic et al 2000;Zivanovic and Marinkovic 2003) and Santiago de Chile II (SC and SCL), Puerto Montt (PM and PML), Gilroy I (GI and GIL), Gilroy II (GII and GIIL), Centralia (C and CL), and Bellingham (B and BL) (Prevosti et al 1988;Mestres et al 1990Mestres et al , 1992Mestres et al , 1995Solé et al 2000;Balanyà et al 2003) Thus, each vector represents a point in the genetic space. Mathematically, this genetic space constitutes a manifold with boundary of dimension n ¼ m À 1 (Balanyà et al 2004).…”

Changes in chromosomal polymorphism and global warming: the case of Drosophila subobscura from Apatin (Serbia)

“…Furthermore, several genes that code for heat stress proteins (Moltó et al , 1992) and others involved in thermal adaptation (Laayouni et al , 2007) are located in this arrangement. In addition, the O 3+4 and O 3+4 + x frequencies in the old Apatin population (June 1994) were 53% and 59% lower, respectively, that in all other southern Balkan populations (Jastrebac, June 1993; Petnica, June 1995; Kamariste, June 1996; Zanjic, June 1997; Djerdap, June 2001; Avala, June 2004) (Zivanovic et al , 2002; Zivanovic and Marinkovic, 2003; Zivanovic, 2007; Zivanovic and Mestres, 2010a,b). In contrast, the frequencies of the O 3+4 and O 3+4 + x arrangements in the new Apatin population (2008 + 2009 sample) were no much lower (by 19% and 28%, respectively) than those previously reported for the southern Balkan populations.…”

“…The degree of chromosomal inversion polymorphism in the population analyzed was assessed using the index of free recombination (IFR) (Carson, 1955). Chromosomal inversion polymorphism patterns were obtained by computing Nei’s genetic distances (Nei, 1972) between Apatin 2008+2009 and Apatin 1994 and another five previously analyzed Balkan populations (Kamariste, June 1996; Djerdap, June 2001; Petnica, June 1995; Jastrebac, June 1993; Zanjic, June 1997) (Zivanovic et al , 2002; Zivanovic and Marinkovic, 2003; Zivanovic, 2007). …”

“…Consequently, the Apatin D. subobscura population has existed in a very humid habitat that has never been changed by man. This is probably the main reason for the large differences observed between the Apatin and other D. subobscura populations from the Balkan Peninsula (Zivanovic et al , 2002; Zivanovic and Marinkovic, 2003; Zivanovic, 2007; Zivanovic and Mestres, 2010a,b). …”

O-chromosome lethal frequencies in Serbian and Montenegrin Drosophila subobscura populations

“…Other previously collected Balkan D. subobscura populations that were used in the present study were from: Petnica, Kamariste, Zanjic and Djerdap. The environmental conditions and the trapping dates at these localities are described in [22,23].…”